1. Field of the Invention
The present invention relates to the summation of the power values coming from several amplification cells for the supply, at a single output, of a transmission signal.
2. Discussion of the Background
The total efficiency of a transmitter depends on the efficiency of the amplification cells themselves as well as the power lost in the different steps of recombination of the elementary power values given by these same cells. It is possible to bring these two points into play to improve the total performance characteristics of the transmitter. However, it is necessary to comply with the requirements of amplitude and phase linearity as well as the functions required of transmitters, such as the interchangeable character of the modules during operation and their standardization.
Class A amplifiers, namely amplifiers whose transistors or other amplifiers components are conductive for 100% of the time, give the most linear signal at output but with a relatively mediocre efficiency. To improve this efficiency, it is possible to make these transistors work in class AB mode with push-pull type assemblies. These assemblies are quasi-linear but the efficiency remains low. In this type of assembly, it is the modulated signal that is amplified.
Amplifiers working in class C mode or, better still, selection-switching mode have an ideal efficiency close to 1. It is therefore valuable to use this type of assembly to obtain high overall efficiency. There are transmitters where the working of all or part of the amplifier cells is controlled to give the amplitude-modulated and phase-modulated output signal in certain discrete levels in order to obtain the constellation of the digital signal to be transmitted. This type of assembly does not give a continuous output signal and, often, the efficiency of the recombination is not optimized.
There are transmitters implementing amplification cells with different elementary power values. A power of any value may then be subdivided more finely on the basis of the power values available. These assemblies require a large number of different types of cells giving rise to high cost price. Here again, the recombination efficiency is not optimized.
There also exist radio-broadcasting amplifiers with amplification cells that are all identical, working in class C mode. The modulation is obtained by the addition of the elementary voltages of each cell. For this purpose, the cells may or may not deliver a voltage, along a bar, by inductive coupling. In this type of device, the cells are interdependent. This rules out the replacement of faulty cells, if any, during the working of the transmitter.
It is aim of the present invention to prevent or at least reduce the drawbacks referred to here above.
This is obtained by an amplitude and phase control of the amplification cells, each capable of giving at least two output levels.
The invention proposes, to this end, a method for preparing a transmission signal with an instantaneous amplitude A and an instantaneous phase xcfx860, by means of n amplification cells, with n as a whole number at least equal to 2, each amplification cell giving a whole number, at least equal to 2, of output discrete levels, including the level zero, characterized in that, considering the primary vector of the modulus A with an argument xcfx860, it consists in determining n secondary vectors with a vector sum equal to the primary vector, these secondary vectors being chosen in a one-to-one relationship with the n cells and each having a modulus with a value corresponding to one of the discrete levels of the cell with which it is in a one-to-one relationship and a phase, in controlling each of the n cells so that it gives a signal with instantaneous amplitude and phase whose values correspond respectively to the values of the modulus and of the argument of the secondary vector in a one-to-one relationship with the cell considered and in summing up, in an energy-coupling device, the signals given by the n cells.
According to the invention, there is also proposed a transmitter for the transmission of a signal with an instantaneous amplitude A and an instantaneous phase xcfx860 comprising a radiofrequency oscillator, n amplification cells with n as a whole number at least equal to 2, each amplification cell giving a finite whole number, at least equal to 2, of output levels, including the zero level, a transmission antenna and an energy-coupling device to couple the antenna cells, characterized in that it comprises computation means to determine n vectors in a one-to-one relationship with the n cells such that their sum is equal to a vector with a modulus A and an argument xcfx860 and in that the modulus of each of them has a value equal to the value of one of the discrete levels of the cell with which the vector is in a one-to-one relationship, amplitude control means to impose, on each cell, the discrete level thus defined by the modulus of the vector associated with the cell considered and phase control means in order to impose on each cell, from the phase of the oscillator, a phase shift equal to the argument of the vector associated with the cell considered.